In a mobile body such as a fuel cell vehicle on which a fuel cell system is installed, a collision sensor such as a G-sensor, that is an acceleration sensor, is usually provided to detect the collision of the mobile body (see JP 2001-119815 A, JP 2004-349110 A, JP 2001-357863 A, and JP 2006-182300 A). In the mobile body disclosed in JP 2001-119815 A, when the collision sensor detects the collision of the vehicle, as a subsequent countermeasure, the development of an airbag and the stopping of hydrogen supply to a fuel cell are executed. In this case, as a certain example, an acceleration sensor for use in an airbag system is used as the collision sensor to judge the presence of the collision from the detection signal of the collision sensor. Moreover, in another example, acceleration sensors installed in a hydrogen storage tank and a fuel cell stack are also used as collision sensors to judge the presence of the collision from the detection signal of at least one of three acceleration sensors.
The vehicle sometimes experiences impact owing to road surface interference or the like during traveling, instead of the collision. In a case where the presence of the collision is judged only by use of the detection signal of one acceleration sensor as in JP 2001-119815 A, the road surface interference or the like might be wrongly judged as the “collision” and, as a result, the development of the airbag might be executed. When a threshold value for use in judging the collision is set to be large, the wrong judgment can be prevented, but in this case, the missing of the detection might occur. Such a problem is similarly feared even in a case where the detection signals of three acceleration sensors which are same type are individually and independently used. Therefore, it cannot be said that in a conventional technology, the collision judgment as a trigger for executing the collision countermeasure has sufficiently been investigated.